Process for producing enamel, more particularly white clouded enamel



Patented Apr. 1, 1941 orri s PROCESS FOR PRODUCING ENAMEL, MOREPARTICULARLY WHITE CLOUDED ENAMEL Ignaz Kreidl, Cleveland, 01110 NoDrawing. Application August 3, 1937, Serial N 0. 157,229. In AustriaMarch 4, 1937 6 Claims. (c1. 106-36.2)

In the production of enamel, such as for example iron enamel, moreparticularly white clouded iron enamel, the'properties of the slip playan important role in wet enameling. In'the production of the slip theenamel frit is ground with addition of water. During the grinding, inorder to obtain a satisfactory applying capability for the product,usually clay is added, and in fact for coating or covering enamelsusually in a quantity of 6-10%. with a quantity of water which is assmall as possible in order to render it possible to give the mass thedesired consistency for the application by dilution. If an enamel ismade up with too much water then the resulting slip is too thin and theenamel runs as one says in the art, or it stays only very badly. Howeversuch "run? ning of the enamel frequently occurs even Without excessivewater addition. Such "running" enamels are very bad to apply.

In order now to bring such enamel to a condition or to bring it again toa condition so that it will stay, one has recourse to so-calledadjusting agents.

which is of varying degree with the different ad'- justing agents, butin certain substances may go so far that the slip sets to a stiff masswhich can be no longer worked by the wet enameling process. As suchadjusting agents exclusively electrolytes come into consideration, e. g.chlorides and sulphates of magnesium and ammonium, carbonates, and soforth.

However by varying the composition of the enamel frit one can alsoarrive at slips which stay too strongly and therefore cannot be satis-Lfactorily worked by the wet enameling process or at least are no longercompatible with, or are not influenced by, additions having an adjustingaction. This is more particularly important inasmuch as for covering orcoating enamel in addition to clay the clouding agent is also added onthe mill and many clouding agents or other indis pensable additionsexert an adjusting action on the mill-i. e. set up the slip-and by thisaction impair the applicability of the enamel slip. More particularlythis plays a role in gas cloudings for which also clouding agents comeinto considera-' tion which are capable of exerting an adjusting effect,so that for such gas clouding agents on the one hand enamel frits whichin the slip already stay strongly cannot be satisfactorily worked up, onthe other hand, slips also are disadvantageous which already withindispensable additions The grinding usually takes place The adjustingaction of these agents exerts itself in a thickening of the enamel slip,

are too strong staying and therefore cannot be satisfactorily worked up.

Such slips which stay too strongly and which cannot be worked upforthwith in the wet process, more particularly slips in which this'toostrong staying power is caused either by the composition of the enamelfrit or by indispensable additions on the mill, or both by suchadditions as well as by the composition of the frit, also cannot be madecapable of application by dilution with water. Even if one can obtainsufficient viscosit'y'by addition of water then in the case of suchslips, a coating free from streaks is not possible. It is, however,possible to obtain a coating free from streaks by dilutingcorrespondingly more strongly, but such strong dilution has the effectthat only insuificient layer thicknesses can be obtained, that is to saythe layer thickness is too small. Moreover drawbacks arise during dryingwhen using such slips.

The present invention depends upon the discovery that in the case ofsuch slips having too powerful staying power, more particularly suchslips of too strong staying power which by dilution alone cannot bebrought to the necessary state of adjustment, the cause for thisphenomenon obviously lies in the too high thixotropy.

According to the invention these drawbacks brought about by too highthixotropy of the slip are removed by the addition of certainelectrolytes having action contrary to that of the adjusting effect. Theinvention in fact depends upon the discovery that by addition of certainsubstances to the slip an action can be attained contrary to theadjusting effect, whereby the invention affords a means of adjustingdown slips of too high staying power without excessively increasing thewater addition, and in fact even with small water addition.

This action according to the invention is produced by the use ofpolyvalent (polybasic) strong acids and in fact the better the highertheir basicity for the same activity, and in fact more particularly thetribasic inorganic and the diand poly-basic organic acids and mixturesof such.

According to the invention also, such acid salts may be employed whichcorrespond to the abovementioned conditions.

Oxalic acid on the one hand, phosphoric acid on the other hand, ormixtures of these substances, best conform to the requirements.

The quantities to be used are found empirically and lie between about 1and 5%.

This invention accordingly enables the field of practical applicabilityfor enamel slips to be considerably widened. On the one hand such slipsmay be made utilisable for the enameling which in consequence of toopowerful staying power hitherto could not be worked or only withdifliculty, and on the other hand the slips capable of being worked upin the usual manner can be improved in their applicability and theworking up ofI-the same with additions on the inill can be madepossible,which hitherto'were out of the question owing to the adjusting actionattending the same. Thus the invention favours" the use of enamel fritswhich in. consequence of their composition yield enamel. slipsv ofpowerful staying powers, such as more particularly enamel frits, whichin the slip show an enhanced colloidal character as compared with normali'n'ately between 1 to 5 parts per thousand.

3. Ina process of. preparing enamel slips comprising adding to saidslips at least one subenamel frits, such as for example enamel frits,which show a fluorine content of about 10% and y I more fluorineoriginating from fluorine come pounds which do not contain aluminium.The invention alsoenables electrolytes orsubstances to be used in spite,of their undesired adjusting acti0n. '-r f- In the process-according tothe present invention, finally there: is the advantage that a uni-..

form drying of the slip applied is ensured.

. The process according to the invention is more particularly suitablefor theproductionof gas cloudedenamel by means of, enamelslips whichcontain .enamel' frits which .as'compared' with normal-frits show in theslip an enhanced colloidal character.

- WhatII .claimis: a

' 1-..A- process for preparing. enamellslipalespcparts of said slip. r

, 5,. An enamel slippf controlled stiffness-hawing incorporatedtherewithoxalic acid ina quan-- titybetween about 1 -,to 5 parts per thousandstance capableof reducing the stiffness of said I slips and selectedfrom the group consisting of polybasic acids and acid reacting saltsthereof} in a.-quantity ranging between 1 to 5 parts per thousand of thesaid slips. 4. An enamel slip of controlled stiffness havingincorporated therewith phosphoric acid in a quantity between aboutl to5v parts per-thousand partsoi said slip.

.6 .An enamel slip of 1 v controlled -stifiness have ingincorporatedtherewith at least one substance capable. of reducing the stiffness ofsaid slip tanid selected from.the group consisting. of

p'olybas'ic acids and acid reacting salts thereof,

in a quantity ranging between 1 to 5 parts per thousand) of the saidslip. v I I IGNAZ KREIDLQ

